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This article discusses a selection of energy saving building retrofit steps including using Air Krete ultralightweight concrete building insulation, sealing leaky sash-weight-operated double hung windows, foam foundation forms, and adding soffit intake ventilation for the roof cavity. Sketch at page top and accompanying text are reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss.

Energy Retrofit Tips & Products

Insulating Existing Wall Cavities with Ultra Lightweight Concrete

The perfect building insulation for retrofitting cavity walls would be non-toxic, non-shrinking, fire-resistant, high in R-value, non-corrosive, and moisture and mold-resistant. It would also have the ability to flow into irregular spaces behind the walls, and be dense enough to stop air leaks. And it's got to be cheap. A product whose use dates to 1983, Air Krete, appears to fit this tall order well.

Air Krete (page top photo) is a cement-based product that weighs about the same as extruded polystyrene - 2 pounds per square foot - and has an R-value of 3.9 per inch. Produced on-site from three components plus water, Air Krete installs much the same way as pump-in foam insulating products. When it dries it is lightweight and crumbly.

According to the company, wet Air Krete will flow in and seal the smallest crevices in a wall, but sets up quickly - within 20 seconds. Because Air Krete hydrates like concrete, when drying it gives off less water than some foam products such as the no-longer used urea-formaldehyde foam insulation (UFFI). Independent testing showed that this concrete wall insulating product shrinks less than 0.25 percent and it is virtually fireproof. [At the time of the original article - see links above - product testing for water-vapor permeance and water absorption were incomplete.]

Because this ultra lightweight concrete has over 80 percent closed cells, the company described it (back in 1985) as similar to expanded polystyrene foam insulation in its reaction to water - that is, it should be a moderate water vapor retarder and a slow absorber of actual water.

Air-Krete is available through licensed installers. Doing a good job is not difficult, but requires a close watch of the equipment. On a good day, a three person crew can put in 14,000 board feet of this insulating material. Cleanup is easy since the raw materials are water soluble.

Prime applications of lightweight concrete insulation include brick cavity wall construction and masonry block cores. For wood-framed building walls, lightweight concrete will get tough competition from blown-in chopped fiberglass or cellulose insulation. Those products can be blown into building walls for about half the cost of lightweight concrete. In 1985 Air Krete installed for $1.25 to $1.50 per square foot in a 2x4 wood framed wall. (1985 prices - check for current costs).

But if high R-values are needed or if you are concerned about settling, fire resistance [seems less a concern with masonry walls], or moisture absorption, Air Krete or similar ultra lightweight concrete wall insulating products are worth looking into. Also these products maybe code-approved for fire stops and fire-walls.

Retrofits for Stopping Drafts at Double-Hung Windows & Window Sashes

Weathersealing an old double-hung window is no one's idea of a good time. Retrofit contractors have found a cheap and simple device that makes that task easier: the Quiki window control. Other window sash controls include an aluminum track that tacks into the existing window sash opening after you remove the parting strips that will be found between the existing sashes. The Quiki window control, or spring-loaded sides of the window track insert will hold the sashes firmly in any position.

An alternative to the window track, if you're just using the window clip, is the installation of plastic V-strips along the bottom sash at the meeting rail and against the parting strips found between the house-interior faces of the stops and the lower sash. Some retrofitters caulk the top sash in place, but if you use the track insert we have cited, that won't be needed.

These products mean you can remove the window sash cords, pulleys, and sash weights from the wall cavities found on either side of older double-hung window sashes, adding foam or fiberglass insulation in those spaces to eliminate what amounts to an un-insulated building wall area on either side of every window. Adding insulation using foam squirted into the cavity will be most effective in stopping drafts. To avoid springing the sides of some less-rigid window frames it may be necessary to wedge a stick between the window opening sides while the foam cures.

Foam Foundation Forms

There are presently a wide variety of foam foundation form manufacturers whose products combine fast concrete forms that also insulate the foundation perimeter. Back in 1985 a leader in this approach was Branch River Plastics who used expanded polystyrene to produce Fast Forms.

Polystyrene insulating concrete foundation form products lend themselves to sunspace construction or other small slab-on-grade jobs where you want to get the backhoe and mixer in and out in a hurry. Fast Forms and similar foam foundation insulating forms come in 4 x 8 foot sections that lock together with dovetail keys and special corners.

The foam foundation forms are engineered to work without rebar in normal soils with typical loads. Concentrated point loads go on special pier forms that fit to the standard sections. After pouring the forms are left in place to insulate the perimeter of the concrete slab.

Because the foam foundation forms are left in the ground, the trenches need to be only 18 to 24 inches wide and can be backfilled as soon as the forms are set. Footing, slab, and wall are poured monolithically, so only one concrete delivery is required. The foam foundation forms help the concrete cure well by retarding the heat and water of concrete hydration. The insulation also helps in cold-weather concrete slab pours.

At their introduction in the 1980's these foam foundation forms cost about $10.40 per lineal foot, but they save on concrete and labor.

Adding Soffit Intake Vents

In several InspectAPedia articles we have emphasized the importance of effective under-roof ventilation to prevent moisture and mold in roof cavities as well as to avoid inadvertently sucking heat out of the building (by providing traditional exit vents or gable end vents without intake venting.

Roof Venting: Soffit Intake Vent-Continuous emphasizes that continuous soffit intake venting is essential for roof ventilation to work properly. In the sketch at left you'll see little round holes drilled through the soffit, covered by a soffit vent strip that can be purchased inexpensively at any building supply house.

DON'T RELY ON LITTLE HOLES in the soffit. Having inspected thousands of homes and seen many attic moisture and ice dam problems on homes where a variety of roof venting systems were installed, we are convinced that what is needed is a continuous opening along the full length of the soffit. Typically the opening is cut about 2" wide - to match the soffit vent strip minus its support flanges. Using a circular saw overhead risks sawdust in the eye, so wear protective goggles. But don't take any shortcuts - it won't work.

Original article

"Eight Retrofit Problem Solvers - new products, time tested techniques, and shortcuts make the hard work of insulation or energy retrofitting a little easier" - provided in original PDF form in the links below, and expanded/updated in text just below.

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Technical Reviewers & References

Solar Age Magazine was the official publication of the American Solar Energy Society. The contemporary solar energy magazine associated with the Society is Solar Today. "Established in 1954, the nonprofit American Solar Energy Society (ASES) is the nation's leading association of solar professionals & advocates. Our mission is to inspire an era of energy innovation and speed the transition to a sustainable energy economy. We advance education, research and policy. Leading for more than 50 years.
ASES leads national efforts to increase the use of solar energy, energy efficiency and other sustainable technologies in the U.S. We publish the award-winning SOLAR TODAY magazine, organize and present the ASES National Solar Conference and lead the ASES National Solar Tour – the largest grassroots solar event in the world."

Steve Bliss's Building Advisor at buildingadvisor.com helps homeowners & contractors plan & complete successful building & remodeling projects: buying land, site work, building design, cost estimating, materials & components, & project management through complete construction. Email: info@buildingadvisor.com
Steven Bliss served as editorial director and co-publisher of The Journal of Light Construction for 16 years and previously as building technology editor for Progressive Builder and Solar Age magazines. He worked in the building trades as a carpenter and design/build contractor for more than ten years and holds a masters degree from the Harvard Graduate School of Education.
Excerpts from his recent book, Best Practices Guide to Residential Construction, Wiley (November 18, 2005) ISBN-10: 0471648361, ISBN-13: 978-0471648369, appear throughout this website, with permission and courtesy of Wiley & Sons. Best Practices Guide is available from the publisher, J. Wiley & Sons, and also at Amazon.com

The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.

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